JP-2002-23761A discloses a drive circuit connected to a sound generating body and having an error determination circuit for detecting an open-circuit in the sound generating body. The error determination circuit measures a current and a voltage of a magnetic coil of the sound generating body.
JP-2003-274491A discloses an open-circuit detection device for detecting an open-circuit in a speaker. The open-circuit detection device includes an equivalent circuit having equivalent impedance to the speaker circuit and detects the open-circuit by comparing an impedance of the equivalent circuit with an impedance of the speaker circuit.
JP-2007-37024A discloses a speaker line testing device for detecting an open-circuit and a short-circuit in a speaker circuit by measuring an impedance of the speaker circuit.
JP-2011-70561A discloses an alarm device including a switch. The switch connects a circuit, which supplies a detection voltage used for open-circuit detection in a piezoelectric sound generating body, to the sound generating body, only when the open-circuit detection is performed.
The error determination circuit disclosed in JP-2002-23761A includes a current transformer and a voltage transformer on a line connected to the sound generating body. Therefore, it is difficult to reduce the number of parts, the size, and the cost of the error determination circuit.
The open-circuit detection device disclosed in JP-2003-274491A includes the equivalent circuit and a switch circuit. Therefore, it is difficult to reduce the number of parts, the size, and the cost of the open-circuit detection device. Further, the open-circuit detection device cannot detect a failure such as an open-circuit during normal operation.
The testing device disclosed in JP-2007-37024A includes a detection circuit for detecting a current in a speaker line. Therefore, it is difficult to reduce the number of parts, the size, and the cost of the testing device.
In the alarm device disclosed in JP-2011-70561A, the detection voltage is supplied only when the detection is performed. Therefore, the alarm device cannot detect a failure such as an open-circuit during normal operation.